One example of a conventional image display apparatus is disclosed in Patent Document 1. To improve contrast, the image display apparatus in Patent Document 1 has a feature detector that detects maximum, minimum, and average luminance levels. The luminance levels are amplified up to the dynamic range. Also provided are a light source and a light source controller; the average luminance, which changes when the luminance levels are amplified, is controlled by controlling the light source so that the perceived luminance (the perceptual luminance) is the same as before the luminance levels were amplified (see Patent Document 1).
To express image continuity naturally, the maximum, minimum, and average luminance levels in the previous processing are stored and compared with the average luminance level of the current input to see how much change has occurred. When the change is small, the time constant of the low-pass filter (LPF) through which the control data pass is increased; when the change is large, the LPF time constant is reduced.    Patent Document 1: Japanese Patent No. 3,215,388 (paragraphs 0011 to 0013 and FIGS. 1 and 2)